Ben is 5 times as old as Christopher and is also 16 years older than Christopher. How old is Christopher?
Explanation: We can use the given information to write down two equations that describe the ages of Ben and Christopher. Let Ben's current age be $b$ and Christopher's current age be $c$ $b = 5c$ $b = c + 16$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $c$ , and both of our equations have $b$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $5c$ $-$ $ (c + 16)$ which combines the information about $c$ from both of our original equations. Solving for $c$ , we get: $4 c = 16$ $c = 4$.